1. Field of the Invention
The present invention relates to a conversion apparatus, and more particularly to a conversion apparatus for converting license information, which controls use of content data in a terminal apparatus.
2. Description of the Background Art
In recent years, content distribution has been familiarized by broadband networks such as the Internet and flat-rate connection environments. Since protection of rights concerning content data (e.g., copyrights or sales rights) is vital to a further prevalence of such content distribution, various right management technologies have conventionally been researched and developed. In the present specification, any rights concerning content data will be referred to as “digital rights”. A representative right management technology is DRM (Digital Rights Management). Hereinafter, a content distribution system incorporating DRM will be described.
To a conventional content distribution system, a server and terminal apparatuses are coupled so as to be capable of data communications via a network. The server stores at least one set of content data, a content decryption key, and license information. The content data, which may be digital data representing music, for example, is encrypted by a predetermined scheme. The content decryption key is a key for decrypting encrypted content data. In the case of DRM, the license information represents usage rules for the content data. Atypical example of a usage rule is a number of times of using the content data.
In a content distribution system having the above structure, content data is distributed as follows. First, a terminal apparatus requests the server to distribute content data. In general, a request for content data is made by a terminal apparatus transmitting a content identifier and terminal-specific information to the server via the network. The content identifier is information which uniquely identifies the content data. The terminal-specific information, which is previously retained in the terminal apparatus, is information which can uniquely identify the terminal apparatus which has made the request for the content data.
In response to the request from the terminal apparatus, the server encrypts the content decryption key by using the currently-received terminal-specific information. Thereafter, the server transmits the encrypted content data, the content decryption key which has been encrypted with the terminal-specific information, and the license information to the terminal apparatus. The terminal apparatus receives the content data, the content decryption key, and the license information which have been distributed from the server, and stores them in an internal memory device.
After storing the above, the currently-decrypted content data becomes usable to the user of the terminal apparatus. When actually using the content data, the user so instructs the terminal apparatus. In response to this instruction, the terminal apparatus operates as follows. The terminal apparatus determines whether or not the current use complies with a usage rule represented by the license information within the memory device. The terminal apparatus performs the subsequent processes only when the usage rule is complied with. Next, since the content decryption key within the memory device is encrypted, the terminal apparatus decrypts the content decryption key by using the terminal-specific information retained therein. Furthermore, since the content data within the memory device is also encrypted as described above, the terminal apparatus decrypts the content data by using the decrypted content decryption key, and thereafter reproduces the decrypted content data.
Next, the problems of the above-described content distribution system will be described. The user of the terminal apparatus (hereinafter referred to as the first user) may desire to pass his or her own license information, i.e., a license for content data, over to another user (hereinafter referred to as the second user). However, the second user may not necessarily be subscribing to the aforementioned content distribution system, and may be subscribing to another content distribution system. Furthermore, the structure of the license information may differ between the two content distribution systems. As a result, even if the second user's the terminal apparatus can receive the license information from the first user's terminal apparatus, it cannot interpret the received license information. Therefore, under the conventional content distribution system, it is impossible to pass one's own license information over to others.
Moreover, a user may be subscribing to different first and second content distribution systems, and may possess a first terminal apparatus which can only interpret license information obtained from the first content distribution system and a second terminal apparatus which can only interpret license information obtained from the second content distribution system. In such a situation, as described above, the structure of the license information used may differ between the first and second content distribution systems. Therefore, even if the second terminal apparatus can receive the license information from the first content distribution system, the second terminal apparatus cannot interpret it. Therefore, in the above situation, it may be possible that the license information owned by a user cannot be utilized on his or her own terminal apparatus.